Kro was a Levithian guard under the Graff Vynda-K. After the Graff returned home to Levthia after the Alliance Wars, he discovered his half-brother was king.

They later travelled to Ribos to attempt to buy it from Garron. When the Graff discovered he had been tricked, he imprisoned Garron, the Fourth Doctor and Romana I inside his room and Kro was ordered to guard the door. When K9 arrived, he stunned Kro, and said he would recover in a few hours. (TV: The Ribos Operation)